Application of films



Dec. 14, 1965 w. R. MCKEIRNAN ETAL 3,223,569

APPLICATION OF FILMS Filed April 2'7. 1961 INVENTORS Will/21m R, Make/man Leo/lard .D. Sana/end ATTORNEY United States Patent ration of Delaware Filed Apr. 27, 1961, Ser. No. 106,080 Claims. (Cl. 156294) This invention relates to the process of wrapping films on base materials and particularly to the application of electron emissive materials onto a cathode base.

In the fabrication of cathodes of the type used in electron tubes, it has been found that pre-cut films of potentially emissive material like the triple earth carbonates dispersed in a soluble binder can be wrapped about a metal cathode base by mere contact of the film with a portion of the base which has been Wetted with a volatile solvent for the binder. The self-wrapping operation follows immediately after contact is made. The base employed generally has a continuous regular convex curvature. However, it has been found that if the surface is irregular, as where it has hollows or protuberances thereon, the film will not readily adhere to all parts of the surface. Also, on occasion, it has been found that even where the surface has a regular curvature, the ends of the Wrap applied to the base metal may not be completely brought into contact therewith, thereby resulting in defective cathodes. Also, where the base surface is flat or where only a patch of emissive film is to be applied to a base, the consistent effectiveness of the wrapping or attachment operation of the film to the base is somewhat reduced when the base is wetted with the solvent in the previous manner.

The defective application of the emissive materials or films to the cathode base metal is apparently due to excessive volatilization of the solvent prior to application of the film to the base metal or non-uniformity of wetting of the metal or bridging of the film over hollows in the metal or between protuberances, or any combination of these causes.

It is an object of this invention to improve application of the film to the base metal by subjecting preferably both the film and metal to a hot volatile solvent vapor for the binder in the film. As a result of this method, the hot solvent vapor penetrates, wets and softens the film which will then be drawn into contact with the surface of the metal base of the cathode. Since the vapors applied are hot, the cathode bases with emissive coating thereon need not be subjected to an independent drying step, as in the past.

The emissive film used in the production of cathodes may but need not have a composition of the type described in the application entitled Powdered Metal Film Composition Lambert and McKeirnan, filed April 27, 1961 and bearing Serial No. 105,889. This film employs potentially emissive materials like the earth carbonates and a combustible binder as well as other materials. For optimum results in securing the drying effects Where the binder in the film is an organic material such as ethyl cellulose, the solvent preferably is a volatile or ganic solvent with low specific heat and it should be a good solvent for the films binder. While toluene will give satisfactory results, it has presently been found more toxic than desired for the use intended. A mixture of alcohols, however, is non-toxic, but requires greater control over the temperature of the vapors. A solvent yielding excellent results is ethyl acetate or Pentacetate, which comprises a mixture of N-amyl acetate, Z-methyl butyl acetate, 3-methyl butyl acetate, 4-methyl butyl acetate, and 3-ethyl propyl acetate and is sold by the Sharples Chemical Company as pentane grade amyl acetate.

Patented Dec. 14, 1965 The Pentacetate boils fractionally between 126 C. and 150 C. with practically all of the solvent in the form of a hot dry vapor at 145 C.

The following table gives the distillation of Pentacetate under standard conditions and at 1150 feet elevation:

Standard Actual at 1150 feet elevation Above 126 C. 99%

C. 95% 93.8% C. 75% 88.7% C. 25% 50% 150 C. None 3.3%

Thus, if a temperature above 140 C. and below 150 C. be maintained, there will exist, in a confined space, a hot solvent vapor for the ethyl cellulose. In practice it has been found that with a temperture of C. in the chamber, the vapor is in a hot dry state. Such a temperature may be maintained within the chamber by an auxiliary heater under thermostatic control.

In carrying out the invention, the Pentacetate" may be continuously distilled into a chamber provided, as at the bottom thereof, with an opening for the admission and withdrawal of the film and of the metal base to be properly coated with the film. The film and metal base, prior to introduction into the chamber, may be at room or a relatively cool temperature. In the circumstance where the film is in contact with the base and the two are introduced into the chamber, the first effect occurring within the chamber is a condensation of the hot vapors on the cooler film and base with consequent wetting of the base with the amyl acetates and softening of the binder in the film. In this condition, all portions of the film will contact and adhere to the metal of the base by virtue of the surface tension effects. Since the vapors and there for the atmosphere in the chamber are still hot, the now coated cathode rapidly rises to the maximum temperature in the chamber and dries. This drying occurs since the cathode temperature is above the boiling point of the solvent. Upon removal of the cathode from the chamber, it is found to be properly coated regardless of the surface configuration. Any condensate forming within the chamber may be permitted to drain therefrom in any suitable manner.

In the accompanying drawing, there is illustrated in diagrammatic form an apparatus for carrying out the process. The apparatus comprises a vaporizing tank 10 containing the Pentacetate and is provided with a drain cock 12, a valved Pentacetate supply pipe 14, and a vapor conducting conduit 16 suitably heat insulated with a jacket 18. The tank also has mounted therein a thermostat 20 connected to a relay 22 whose armature 23 controls the application of heating current to a heating coil 24 suitably associated with the tank 10 as by being incorporated with the walls thereof.

The conduit 16 directs the Pentacetate vapor from tank 10 to a vapor containing chamber 30 having a drainage bottom 32 sloping toward a drainpipe 34 provided with a hose 36 leading to a solvent recovery tank (not shown). Mounted within the chamber 30 is a second thermostat 38 controlling a second relay 40, whose armature 42 controls the heating circuit to a chamber heating coil 44, here shown as embedded in the wall of the chamber. Within a restricted area of the bottom of the chamber is a small opening 46 to permit the introduction of separated cathode bases and emissive films or introduction and removal of a cathode metal base with an emissive coatng positioned thereabout and which may be imperfectly previously applied to the metal base.

An indexible conveyor 50 moves beneath the opening in chamber 30, the conveyor having recesses 52 to accommodate the ends of the cathode, there being a cross bar 54 across the bottom of each recess to prevent the cathode from falling through the conveyor. Movable during the rest period of the conveyor is a transfer fork 60 comprising two tines 62 and 64 to straddle the bar 54 while the fork is rising. The upper end of each tine is reduced in size to form a shoulder 66 to engage the lower edge of the cathode and a needle portion 68 extending above the shoulder to lie within the cathode base, which may be a hollow sleeve.

When the process is used to provide a final proper wrapping, the conveyor may have positioned thereon several types of improperly applied cathode films. Thus, cathode 70 may have a diagonal corner of the film unattached to thecathode metal. Cathode 72 is shown with a hollow portion in the sleeve to which the film has not become attached. Cathodes 74 and 76 have an edge of the film unattached to the metal of the cathode. Cathode 78 shows a cathode after vapor treatment and with the film properly attached to the metal. The period of time which is required for a cathode to be spent in the chamber 30 depends upon the size of the cathode, the thickness of the film and other factors, but generally is of the order of a few seconds. The proper time can be determined empirically for any given cathode and coating by noting the condition of the cathode after vapor treatment.

The process described herein is applicable to providing proper Wrapping of the cathode film about the metal sleeve after the film has been attached at least in part to the sleeve. This invention also contemplates a wrapping or attaching operation wherein the film and sleeve are brought into contact but not attached before application of the vapor. Also, the film and sleeve may be moved into contact after the film or sleeve or both the film and sleeve have been subjected to the solvent vapor treatment. .The vapor may be confined within a chamber as shown in the drawings or it may be applied to the film and sleeve in other ways such as by issuing from properly positioned nozzles.

Although the invention has been illustrated in conjunction with final wrapping of cathode sleeves, it is contemplated to include wrapping or attaching any coating or patch, whether it be electron emissive or otherwise, to another surface having any configuration with the utilization of a solvent vapor for one or more constituents in the film or layer composition.

Although several embodiments of the invention have been shown; and described, it will be apparent to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the, invention as defined by the appended claims.

What is claimed is: v

1. The process of applying a film containing potentially electron emissive material and an ethyl cellulose binder therefor to a cathode base metal comprising subjecting said film and base, while in contact and at cool temperatures, to the effects of a hot dry atmosphere containing a mixture of isomeric amyl acetates whereby initially some of the acetates condense upon the cool metal and film to effect a complete adherence of the film to the metal and, subsequently, to dry the metal and film, and then removing the resulting fithQd? fIQ l said atmosphere.

2. In a process of applying a film to an object having a cool surface and wherein the film includes a soluble binder, the step comprising subjecting said film and object while in contact to a hot vapor containing a solvent for the binder until the film has attached itself to the object.

3. The process of applying a film to an object having a cool surface and wherein the film has a soluble binder, comprising subjecting said film and object while in contacting relationship to an atmosphere of hot dry vapor containing a solvent for the binder, said solvent condensing on said cool surface and initially wetting the film and cool surface, and maintaining said object and film within the atmosphere until the film has attached itself completely to the object and has become substantially dry.

4. The process of applying a film to an object having a cool surface and wherein the film has a soluble binder, comprising subjecting the film and object while in contacting relationship to an atmosphere of hot dry vapor at between C. and C. and containing a solvent for the binder, said solvent consisting of a mixture of isomeric amyl acetates, and maintaining said object and film within the atmosphere until the film has attached itself completely to the object and has become substantially dry.

5. The process of applying a film containing an organic binder and potentially electron emissive material to a cathode metal base comprising preliminarily assembling the film and the base, said film and base having initial temperatures and then subjecting both the film and base to an atmosphere of hot dry vapor substantially above said initial temperatures, said vapor containing organic solvents for the binder in the film, maintaining the film and base within the atmosphere until the film and base have been wetted by the hot solvent condensing thereon, contacting the film and base to effect complete adherence of the film to the base and until the base and film have heated up sufficiently to evaporate the condensed vapor and become dry, said film and base having initial temperatures below the condensation temperature of the solvent, and finally removing the treated film and base from the vapor atmosphere.

References Cited by the Examiner UNITED STATES PATENTS 1,633,577 6/1927 Franks 156-306 XR 2,125,874 8/1938 Anderson 18-59 2,202,025 5/1940 Reed 156-306 XR 2,281,646 5/ 1942 Whitehead 156-305 2,334,232 11/1943 Wells 12-415 2,377,208 5/1945 Card 12-41.5 XR 2,403,313 7/1946 Taylor 156-305 2,660,547 11/1953 Robertshaw 313-346 2,813,051 11/1957 MacHenry 156-305 XR 2,986,671 5/1961 Kerstetter et al 156-497 2,998,052 8/1961 Roeber 313-346 XR EARL M. BERGERT, Primary Examiner.

C RL F,- KRA FT, Examiner. 

1. THE PROCESS OF APPLYING A FILM CONTAINING POTENTIALLY ELECTRON EMISSIVE MATERIAL AND AN ETHYL CELLULOSE BINDER THEREFOR TO A CATHODE BASE METAL COMPRISING SUBJECTING SAID FILM AND BASE, WHILE IN CONTACT AND AT COOL TEMPERATURES, TO THE EFFECTS OF A HOT DRY ATMOSPHERE CONTAINING A MIXTURE OF ISOMERIC AMYL ACETATES WHEREBY INITIALLY SOME OF THE ACETATES CONDENSE UPON THE COOL METAL AND FILM TO EFFECT A COMPLETE ADHERENCE OF THE FILM TO THE METAL AND, SUBSEQUENTLY, TO DRY THE METAL AND FILM, AND THEN REMOVING THE RESULTING CATHODE FROM SAID ATMOSPHERE. 